9p: drop unused declaration from coth.h

Commit "ebac1202c95a virtio-9p: use QEMU thread pool" dropped function
v9fs_init_worker_threads.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/9pfs/coth.h

@@ -47,7 +47,6 @@
     } while (0)
 
 extern void co_run_in_worker_bh(void *);
-extern int v9fs_init_worker_threads(void);
 extern int v9fs_co_readlink(V9fsPDU *, V9fsPath *, V9fsString *);
 extern int v9fs_co_readdir_r(V9fsPDU *, V9fsFidState *,
                            struct dirent *, struct dirent **result);